The present invention relates to a rotor of a hydraulic machine, preferably a Francis turbine, Francis pump-turbine or radial or diagonal pump, with a number of rotor blades which are arranged between an inner and an outer cover disk, and the rotor blades having an inlet edge and an outlet edge.
A rotor of a hydraulic machine, for example, a Francis turbine, is shown in FIG. 4 hereof. It has a plurality of rotor blades 1, each having an inlet edge 4 and an outlet edge 5. The blades 1 are arranged between an inner cover disk 3 and an outer cover disk 2. Two blades 1 forming a flow duct for an operating medium, for example water, and the operating medium flows through the duct during the operation of the hydraulic machine and thus sets the rotor in rotation. The manufacture of such a rotor is highly complicated because of the complex geometric shapes of the rotor blades. In order to allow the manufacture of the rotor, for example by welding, etc., and/or a corresponding machining of the surfaces, for example by grinding, polishing, etc., by means of machine tools, such as, for example, robots, etc., the rotor blades should not lie too closely to one another. Furthermore, when blade regions are closely adjacent to one another, there is always the risk that flushed material will remain caught in the rotor and therefore will be detrimental to operation or may even make it necessary to shut down the hydraulic machine.
On the other hand, a small radius at the inner cover disk is desirable in the region of the outlet edge (=inlet edge in the case of a pump-turbine in pumping mode) of the rotor blades, since this is advantageous for operation, above all at operating points away from the design operating point. In the case of a small radius, for example, vortex formation at the outlet of the rotor would be improved substantially in the part-load ranges.
A large number of blades results in highly confined space conditions at the rotor outlet. On the other hand, a small number of blades results, at the rotor inlet, in wide spacings and high load and cavitation at the rotor inlet.
In order to eliminate this fundamental contradiction, rotors have been manufactured, for example, such that every second or third blade in the entire outlet region of the rotor blades has been designed so as to be shorter than the adjacent rotor blades, what is known as the “splitter blade runner”, and the rotor blades in the inlet region have generally been left the same. The advantage of this design is that more space has consequently been provided in the outlet region, thereby essentially eliminating the above disadvantages. However, in this case, the risk of cavitation increases in the region of the outer cover disk between the blade center and outlet edge, since the blade loads increase there because of the partially reduced blade lengths.
U.S. Pat. No. 6,135,716 again discloses a rotor of a Francis turbine, in which the cavitation behavior has been improved in that the inlet and outlet edges of the rotor blades are shaped in a special way with respect to the axis of rotation of the turbine. The lengths of all the rotor blades are in this case left the same and therefore correspond to a conventional rotor. This results, however, once more in the abovementioned disadvantages with regard to manufacture and operation away from the design operation point.